<div id="some" class="some">
<label for="some">Заголовок</label>
<p>
<label>
<input type="radio" class="input_radio" name="some_radio" value="0"
checked="checked">
<span class="radio-custom"></span>
<span class="label">Выбрать 0</span>
</label>
</p>
<p>
<label>
<input type="radio" class="input_radio" name="some_radio" value="1">
<span class="radio-custom"></span>
<span class="label">Выбрать 1 </span>
<input type="text" class="input" name="price" value="">
</label>
</p>
</div>
...
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script>
$( function()
{
$('.input').bind( 'focus', function () {
$( this ).siblings('.input_radio').prop('checked',true)
} )
});
</script>